An efficient fire place is herein defined as having an insulated combustion chamber and a large non-gasketed glass door so as to provide a full view of the fire with a high percentage of its heat radiated through the glass. U.S. Pat. No. 4,681,087 illustrates such a construction.
When the Clean Air Act authorized the EPA to regulate wood burning, no such product existed. The resulting regulation required a Woodheater to burn a load of 2×4's and 4×4's spaced 1.5″ apart at a very slow rate and defined a fireplace as being very inefficient. Some very clever engineering took place resulting in rather complex, airtight, costly and unattractive units such as described in U.S. Pat. No. 4,766,876.
The overall result was a decline (much greater than anticipated by the regulators) in new wood burning sales except for exempt units such as outdoor boilers. There are no efficient wood burning fire places. The sales of gas and electric fire places have experienced significant growth.
Any fireplace lover knows that the way to get a long burn is with a large “all-nighter” log. To try and slow down a bunch of small logs will result in smoke in the room or dirty glass. An open fire place generally burns cleanly because it has air all around it. A generous controllable air supply is indicated. To be efficient means minimizing the heat sent up the chimney which calls for restricting the flue opening and extracting as much heat as possible before it gets to the flue. To avoid jets of air from leaky doors it is desirable to keep the flue draft as low as possible. This is best done with dilution air. The construction described herein accomplishes these three functions in a user friendly and economical fashion.